Process for heat stable salts removal from solvents

ABSTRACT

An apparatus and a method for removing salts from a liquid are described. A first liquid containing at least one salt is mixed with magnetic composite particles. A subsequent separation of the particles from the liquid is achieved using an electromagnetic source.

The current invention arises from the efforts that have been taken placeas a part of the ongoing project studying removal of heat stable salts(HSS) from solvents. The project is funded by the Petroleum InstituteGas Processing and Materials Science Research Center (GRC). Theseefforts have led to the development of a new method and process for HSSremoval from solvents.

BACKGROUND

There are several processes, i.e. gas sweetening, where it is needed touse solvents, especially amine solvents, to absorb gases such as H2S andCO2. Especially all amine solvents are prone for Heat Stable Saltsgeneration such as sulfates, thiosulfates, chlorides, formates,acetates, oxalates, glycolates, etc. Heat-stable-salts (HSS) are formedin such cases from amine degradation products and some of thecontaminants in the process water mixed with the amine.

Heat-stable-salts (HSS) cannot be removed by conventional regenerationprocess i.e. stripping. The accumulation of these HSS makes the acidgases absorption become less stable. The accumulation of HSS in solventslike amine solvents may lead to the corrosion and fouling of the processequi-pment, and in turn short life of the equipment. Moreover, these HSScontribute to solution foaming which cause the losses of in particularamine and other serious problems. Therefore, the removal of these HSSfrom the amine solvents is especially crucial for amine absorptionprocesses.

Usually, an ion-exchange (IE) method is applied to separate HSS fromamine solvents. See U.S. Pat. Nos. 4,170,628, 4,122,149, 4,113,849 and4,071,602. These patents use ion exchange resins to remove heat stablesalts from amines solvents.

However, the cost of IE method is relatively high. The frequentregeneration of exchange resin may cause serious second pollution due tothe production of acid and alkaline wastewaters. Ion-exchange (IE)method requires a significant amount of acid and base solutions forregeneration, mostly at higher feed salt concentrations, and thisrepresent the major cost of the regeneration process. Furtherregeneration produces a large volume of waste solution which requiresneutralization and disposal. As with new advances in ion exchangeprocesses, the requirements for regeneration chemicals have reduced.Resins degrade over time due to fouling by organics, and suspendedparticles, which requires periodic cleaning and replacement. Inaddition, cationic resins can capture protonated amines thus leading toamine losses. Similarly, if the amine loading is too high, bicarbonateanions can be removed along with the anions of interest.

Another process for HSS removal from amine solvent is Electro dialysis(ED). The use of Electro dialysis (ED) for amine purification isinvestigated in numerous studies. This ED approach was demonstrated toremove contaminants from amine solutions. There are some proposedconfigurations of ED in different patents for solvent reclamation andheat stable salts removal. The patent CA1334836 C involves an ED methodfor removing heat-stable salt from contaminated amine solvents. Thelatter is treated by a base addition to neutralize the heat stable aminesalts prior passing the electrodialysis step.

ED has anionic and cationic membranes; replacing these membranes iscostly, time-consuming, and disruptive, as the flow of the fluid beingprocessed may have to be stopped for a period of time. Further, disposalof used membranes items may not be environmentally friendly. The anionicand cationic ED membranes should have low electrical resistance, andhave high thermal and mechanical stability. The ED electrodes areusually made of titanium and plated with platinum. Electro-dialysis foramine purification is best operated at a low temperature. Neutralizationwith a base such as KOH, or NaOH, and microfiltration are usuallyrequired upstream of the ED unit. Filtration in general can cause lossof amine.

The presence of suspended solids, hydrocarbons, or dissolved iron in theamine solution can cause fouling on the membrane surface, thusincreasing the membrane resistance and reducing the process efficiency.If amine recovery is high, ion removal rates are lowered and ion removalrates is high, amine loss through the membrane is high.

A further disadvantage is that some of the anions and the protonatedamine can be transferred and lost in the process. In addition, theexpected lifespan for anion-exchange membranes is 10 years, and forcation-exchange membranes is 15 years. Many membranes are designed for apH range from 2 to 9, and the typical pH range of lean amine solutionsis pH 9-11 which may cause membrane failure.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus and amethod for heat stable salts removal from solvents, especially fromamine solvents.

It is another object of the present invention to provide an apparatusand a method that can be installed in running units for continuesremoval of HSS from amine solvents.

It is a further object of the present invention to provide an improvedapparatus and an improved method for HSS removal from solvents,especially from amine solvents.

It is moreover an object of the present invention to provide anapparatus and a method for HSS removal from solvents, especially fromamine solvents, which overcome one or more of the aforementionedproblems associated with conventional HSS removal techniques.

In order to achieve one or more of the mentioned objects, the presentinvention provides an apparatus for removing salts from a liquidcomprising:

a first liquid containing at least one salt,

magnetic composite particles,

a tank 2 for storing the first liquid containing at least one salt,

a mixing tank 4 in fluid communication with the tank 2 for mixing thefirst liquid containing at least one salt with the magnetic compositeparticles, and

an electromagnetic separator 5 in fluid communication with the mixingtank 4, wherein the electromagnetic separator 5 comprises anelectromagnetic source 6.

It is preferable for the apparatus according to the invention that thefirst liquid is an aqueous amine solvent, wherein it is more preferredthat amine solvent comprises at least one of methyldiethanolamine andalkanolamine. It is also preferable that at least one salt is formed byone or more protonated amine cations and one or more anions selectedfrom SCN⁻, HCOO⁻, CH₃COO⁻, and CH₃CH₂COO⁻. The magnetic compositeparticles in the apparatus according to the invention preferablycomprise iron oxide magnetic particles and/or alginate.

It is also preferred that the apparatus according comprises one or moreand most preferably all of the following additional materials andcomponents:

a second liquid for cleaning the magnetic composite particles fromadsorbed salt and a tank 3 in fluid communication with the mixing tank 4for storing the second liquid, wherein the second liquid is preferablywater;

a treated liquid tank 7 in fluid communication with the electromagneticseparator 5 for collecting first liquid which has been treated in themixing tank 4;

a collecting tank 8 in fluid communication with the electromagneticseparator 5 and in fluid communication with the tank 3 for collectingthe second liquid containing magnetic composite particles having atleast a portion of the at least one salt adsorbed thereon.

In a particularly preferred embodiment the apparatus according to theinvention has the following features:

the first liquid is an aqueous amine solvent, preferably comprising atleast one of methyldiethanolamine and alkanolamine,

the at least one salt is formed by one or more protonated amine cationsand one or more anions selected from SON⁻, HCOO⁻, CH₃COO⁻, andCH₃CH₂COO⁻,

the magnetic composite particles comprise iron oxide magnetic particlesand alginate,

the apparatus further comprises a second liquid for cleaning themagnetic composite particles from adsorbed salt and a tank 3 in fluidcommunication with the mixing tank 4 for storing the second liquid,wherein the second liquid is preferably water;

the apparatus further comprises a collection tank 7 in fluidcommunication with the electromagnetic separator 5 for collecting firstliquid which has been treated in the mixing tank 4,

the apparatus further comprises a treated liquid tank 7 in fluidcommunication with the electromagnetic separator 5 for collecting firstliquid which has been treated in the mixing tank 4, and

the apparatus further comprises a collecting tank 8 in fluidcommunication with the electromagnetic separator 5 and in fluidcommunication with the tank 3 for collecting the second liquidcontaining magnetic composite particles having at least a portion of theat least one salt adsorbed thereon.

In order to achieve one or more of the afore-mentioned objects, thepresent invention further provides a method for removing salts from aliquid comprising the steps:

providing a first liquid containing at least one salt,

feeding magnetic composite particles to the liquid and mixing themagnetic composite particles with the first liquid, and

separating the magnetic composite particles having at least a portion ofthe at least one salt adsorbed on the magnetic composite particles fromthe first liquid using an electromagnetic source.

It is preferable for the method according to the invention that thefirst liquid is an aqueous amine solvent, wherein it is more preferredthat amine solvent comprises at least one of methyldiethanolamine andalkanolamine. It is also preferable that the at least one salt is formedby one or more protonated amine cations and one or more anions selectedfrom SCN⁻, HCOO⁻, CH₃COO⁻, and CH₃CH₂COO⁻. The magnetic compositeparticles in the apparatus according to the invention preferablycomprise iron oxide magnetic particles and/or alginate.

In a particularly preferred embodiment the afore-described methodaccording to the present invention further comprises a step ofdischarging a mixture of the magnetic composite particles with the firstliquid after mixing the magnetic composite particles with the firstliquid in a mixing tank 4 to an electromagnetic separator 5 where aseparation takes place by which the magnetic composite particles havingat least a portion of the at least one salt adsorbed on the magneticcomposite particles are separated from the first liquid by turning onand using an electromagnetic source 6 which is comprised by theelectromagnetic separator 5.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of collecting the first liquid afterthe separation in a treated liquid tank 7.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of feeding a second liquid, which ispreferably water, as a regeneration liquid from a tank 3 to the mixingtank 4 and then to the electromagnetic separator 5.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of turning off the electromagneticsource 6 and feeding a mixture of the second liquid and the magneticcomposite particles having at least a portion of the at least one saltadsorbed on the magnetic composite particles to a collecting tank 8.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of feeding the mixture in thecollecting tank 8 back to the electromagnetic separator 5 and turning onthe electromagnetic source 6 such that the magnetic composite particlesare trapped in the electromagnetic separator 5.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of feeding the second liquid fromthe electromagnetic separator 5 to the collecting tank 8, and furtherfeeding the second liquid from the collecting tank 8 to the tank 3.

In addition to the foregoing step, the method according to the inventionfurther preferably comprises a step of feeding additional first liquidfrom a tank 2 via the mixing tank 4 to the electromagnetic separator 5,turning off the electromagnetic source 6 and feeding a mixture of themagnetic composite particles and the first liquid to the mixing tank 4.

It is seen that the present invention provides an apparatus and a methodfor HSS removal from solvent, preferably amine solvent, using magneticcomposite microparticles (MOM). In this regard, Heat Stable Salts (HSS)in the solvent, preferably the amine solvent, are adsorbed in MCM andthen removed using electromagnetic separator. The contaminated MCM isthen preferably reactivated and reused. Accordingly, magnetic compositemicroparticles (MCM) are used for HSS removal. Preferably, magneticparticles are prepared and then mixed with a polymer, preferably analginate polymer, so that magnetic composite microparticles areachieved. Amine solvent as used herein refers to a solution, preferablyan aqueous solution, containing one or more amine compounds. Aminecompounds include primary amines, secondary amines, tertiary amines,protonated amines and quaternary ammonium compounds. The organicresidues attached to the amine nitrogen include e.g. alkyls, alcoholsand alkanols. Preferred amines are methyldiethanolamine andalkanolamine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings of which:

FIG. 1 is a schematic diagram for the fully automated process accordingto the invention where MCM are interacted with the treated amine solventthen reactivated and re-injected back for further reuse.

FIG. 2 is an SEM image for the synthesized Iron oxide magneticparticles.

FIG. 3 shows an effect of CaCl2 concentration on HSS removal.

FIG. 4 shows an effect of magnetic composite microparticles dosage onHSS removal.

FIG. 5 shows an effect of temperature on HSS removal using magneticcomposite microparticles.

FIG. 6 shows pseudo-first-order kinetics of a kinetic study ofE-1Fe-Magnetic_1.25M for 4 hours by In(q_(e)-q_(t)) vs. time.

FIG. 7 shows pseudo-first-order kinetics of a kinetic study ofE-1Fe-Magnetic_1.25M for 4 hours by t/qt vs. time.

FIG. 8 shows intra-particle diffusion in a kinetic study ofE-1Fe-Magnetic_1.25M for 4 hours by qt vs. t^(1/2).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally applicable, and is advantageouslyespecially usable for HSS removal from amine solvents. It is used forthe removal of HSS before they accumulate further in the amine solventunit and deteriorate its quality and performance. The present inventionprovides a fully automated method to continuously remove HSS from aminesolvents. Heat Stable Salts (HSS) in a solvent and more preferably in anamine solvent are adsorbed in MCM and then removed using anelectromagnetic separator. The contaminated MCM is then preferablyreactivated and reused. Any industry that needs to remove contaminatesfrom a fluid using magnetic particles can benefit from the proposedprocess. In an especially preferred embodiment, the proposed process canbe integrated readily with running natural gas sweetening absorptionprocesses.

Examples of units where amine solvents come in contact with gas streamand are prone to HSS generation and accumulation include dehydrationunits and gas sweetening units. The present invention can also be usedon amine solvents that are used to process hydrocarbon liquids.

Methyldiethanolamine and alkanolamine solutions in general are used ingas sweetening process to strip acid gases, specifically carbon dioxideand hydrogen sulfide. Amine solvents are characterized by their highselectivity to absorb these acid gases. The acid gases are considered ascorrosive agents; the existence of acid gases with liquid water in theprocess vessels and pipes threatens their structures from corrosion. Theacid gases should be removed and kept below the preferred designspecification of 4-20 ppm H₂S and <3% CO₂.

During the absorption of H₂S and CO₂ by-products such as SCN⁻, HCOO⁻,CH₃COO⁻, and CH₃CH₂COO⁻ are produced by the reaction between oxygen andH₂S and CO₂. These by-products and the protonated amine form a heatstable salt (HSS) system, which could not be removed by systemregenerator. The accumulation of these HSS makes the acid gasesabsorption become less stable. The increase of HSS in solution may leadto the corrosion and fouling of the equipment, and in turn short life ofthe equipment. Moreover, these HSS contribute to solution foaming whichcauses the losses of amine and other serious problems. Therefore, theremoval of these HSS from the amine solvents is crucial for amineabsorption processes.

The present invention can be installed in the lean amine cycle andprovide continuous removal of HSS from amine solvents. The presentinvention introduced the use of magnetic composite microparticles (MCM)to adsorb and remove HSS from amine solvents. HSS can be removed beforethey accumulate in the amine solvent and deteriorate its quality andperformance. The best place to install the presented process 1 in arunning amine unit depends in the unit design and configuration, eachunit should be dealt with separately; however, the best place for gassweetening unit can be on the lean amine stream either before therich-lean heat exchanger to benefit from the high temperature of leanamine around (120° C.) before reducing it down in the heat exchanger orafter the rich-lean heat exchanger.

A particularly preferred continuous HSS removal process 1 has a leanamine tank 2, a cleaning solution tank for MCM reactivation 3, a mixingtank 4 to mix the MCM with the untreated amine solvent, anelectromagnetic separator 5 equipped with electromagnetic source 6, atreated amine solvent 7, MCM regenerating and collecting tank 8, andcentralize control unit 9.

The operation of the process 1 is described with respect to FIG. 1. Thelean amine tank 2 has a solvent inlet that is withdrawn as a side streamfrom the process solvent i.e. the lean amine stream in amine gassweetening unit. The untreated amine solvent is pumped to the mixingtank 4; a MCM is manually added to the mixing tank 4. After sufficienttime in the mixing tank the amine solvent with the MCM are dischargedfrom the mixing tank to the electromagnetic separator 5. Theelectromagnetic source 6 is turned on by the central control unit 9 sothat the contaminated MCM with HSS are trapped in the electromagneticseparator 5. The treated amine solvent then is collected in treatedamine solvent tank 7, the treated amine solvent can then be sent back tothe main unit. The central control unit 9 then will close the treatedtank inlet valve 10, and open the MCM regenerating and collecting tankinlet tank 11.

The regeneration cycle starts by pumping the regeneration liquid fromtank 3 to the mixing tank 4 and then to the electromagnetic separator 5.The electromagnetic source 6 is turned off by the central control unit 9so the contaminated MCM with HSS are washed from the electromagneticsource 6 by the regeneration solution to the MCM regenerating andcollecting tank 8. After sufficient time the regenerated MCM with theregeneration solution are pumped back to the inlet of theelectromagnetic separator 5, the electromagnetic source 6 is then turnedon by the central control unit 9 so that the reactivated MCM are trappedin the electromagnetic separator 5. The regeneration solvent (water) isthen collected in collecting tank 8 and pumped back to the cleaningsolution tank 3 for further reuse.

Then the central control unit 9 will pump untreated lean amine solventfrom tank 2 for washing the reactivated MCM trapped in theelectromagnetic source 6, the electromagnetic source will be turned offby the central control unit 9. The amine solvent with the reactivatedMCM will be recycled to the mixing tank 4 for another cycle of removingHSS.

Magnetic Composite Microparticles (MCM) Syntheses and Testing for HSSRemoval

A homogenized solution of 1.0 wt % alginate is prepared by mixing sodiumalginate in distilled water. Concentration of 1.0 wt % magneticparticles is added to homogenized alginate solution. The magneticparticles are uniformly dispersed in alginate solution by vigorousmixing on a vortex, followed by ultrasound. The resulting suspension isthen added dropwise into CaCl₂ solution (1M) through a micropipette tipby means of a peristaltic pump. The prepared hydrogels beads are left tocure in the calcium bath overnight in order to ensure completepolymerization. Finally after the curing period, the small magnetichydrogel beads are recovered using a magnet and washed several timeswith deionized water to remove the unbound calcium ions. The beads arethen dried for two hours at room temperature and stored for furtheranalysis.

Batch Adsorption for Screening

Adsorption experiments are performed by adding various amounts ofmagnetic alginate microparticles into a 25 ml conical flask containing10 ml of Industrial Lean amine solvent. The flask is then allowed toequilibrate on a water bath at 140 rpm for 4 hours. After reachingequilibrium, the magnetic alginate metal oxide composite beads areremoved from the Lean amine samples using magnetic force and the Leanamine is filtered. The concentrations of HSS in the Lean amine samplesbefore (C_(i)) and after (C_(e)) adsorption are measured using UVI-visspectrophotometer.

The adsorption percentage of HSS (% removal) is calculated usingfollowing equation:

${\%\mspace{14mu}{Removal}} = {\left( \frac{C_{i} - C_{e}}{C_{i}} \right)*100}$

TABLE 1 Removal of HSS using various magnetic alginate compositesorbents LA Weight, Volume, Ci, Ce, % Name of adsorbent g ml ppb ppbRemoval Strontium Ferrite 1.003 10 4630 4030 12.96% Strontium Ferrite2.002 10 4630 3790 18.14% MgFe₂O₄ 1.003 10 4630 4375  5.51% ZnFe₂O₄1.003 10 4630 4235  8.53% ZnFe₂O₄ 2.002 10 4630 3900 15.76% Iron oxideparticle 2.002 10 4630 3770 18.57%

From the screening, it is identified that Iron oxide magnetic particlesare found to have the best removal of total HSS (18.57% for 2.0 g MCM)from industrial lean amine solvent. Hence further optimization, kineticsand thermodynamics are carried out using Alginate/Iron oxide magneticcomposite.

Kinetics and Thermodynamics Study on Alginate/Iron Oxide MagneticComposite Preparation of Iron Oxide Magnetic Nanoparticles

The chemical reagents used for the preparation of iron oxide particlesis Ferric chloride: FeCl₃·6H₂O, Sodium hydroxide: NaOH, and Ethanol.

A typical approach for the synthesis is given as follows: To ahomogenized solution of ferric chloride in water, Sodium hydroxide isadded and vortexed vigorously until a brownish precipitate is formed.The mixture is then placed inside an oven at 85° C. for 10 hours toremove the excess water. After drying, the brown precipitate isseparated by filtration, followed by washing with distilled water.Finally an ethanol wash is performed and the obtained powder particlesare oven dried at 85° C.

Synthesis of Alginate/Iron Oxide Magnetic Composite

Initially 1.0 wt % of magnetic iron oxide particles are added to 1.0 wt% homogenized alginate solution. The mixture is allowed to vortexvigorously followed by sonication using ultrasound. The resultingsuspension is then added dropwise through a micro pipette tip into CaCl₂solution using a peristaltic pump. The prepared hydrogels beads are leftto cure in the calcium chloride solution overnight in order to ensurecomplete polymerization. Finally after the curing period, the smallmagnetic hydrogel beads are recovered using a magnet and washed severaltimes with deionized water to remove the unbound calcium ions. The beadsare then dried for two hours at room temperature and stored for furtheranalysis.

Magnetic Composite Microparticles (MCM) Characterization

SEM analysis was performed to confirm the morphology of the synthesizediron oxide particles. FIG. 2 shows an SEM image of Iron oxide magneticparticles. The obtained image using scanning electron microscopy clearlyshows that the iron oxide particles have spherical shape.

Effect of CaCl₂ Concentration

The effect of the cross linker concentration on the amount of HSSremoval is studied by varying the concentration of CaCl₂ from 0.5 M to2.0 M, while preparing the magnetic composite. As shown in FIG. 3, it isobserved that maximum removal of 21.36% and 21.63% was obtained for aCaCl₂ concentration of 1.25 and 1.5 M respectively. Also it is seen thatfurther increase in concentration above 1.5 M resulted in a decrease inthe removal percentage.

Effect of Adsorbent Dosage

FIG. 4 depicts the % removal of HSS with different dosage of magneticcomposite microparticles (MCM). The HSS removal is found to increasewith MCM dosage.

Effect of Temperature

The % removal of HSS with different MCM dosage at various temperaturesis shown in FIG. 5.—The HSS removal is found to increase with increasein temperature confirming that the adsorption process is endothermic innature. 3.0 g of alginate/iron oxide magnetic hydrogel compositeexhibited a removal of 29.24%, 32.04% and 35.38% at 25° C., 35° C. and45° C. respectively.

Adsorption Kinetics

For predicting the rate of HSS removal using the prepared MCM andestimating the equilibrium time, adsorption kinetics study is performed.For the kinetic study, 1.0 g of MCM is added to each of the conicalflasks containing 10 ml of lean amine at room temperature. At definitetime intervals, the beads are recovered using magnetic force and thelean amine samples are filtered and analyzed using UV-vis for HSScontent. Different kinetics models such as pseudo-first-order,pseudo-second-order and intra-particle diffusion models are studied toanalyze the experimental data. Plots of In(q_(e)-q_(t)) versus time canbe seen in FIG. 6, t/q_(t) versus time can be seen in FIG. 7 and q_(t)versus square root of time is given in FIG. 8. These Figures are made topredict how experimental data fits with pseudo-first-order kinetics,pseudo-second-order kinetics and intra-particle diffusion respectively.From the correlation coefficient values it can be clearly seen that theadsorption kinetics follows pseudo-second-order kinetics with a rateconstant of 0.03696 and this indicates that the removal is chemical innature which is in agreement with the endothermic nature of the batchprocess.

By doing these specific measurements the capacity of CMC for the removalof HSS from amine solvent can be determined. CMC can be prepared fromdifferent composite with different sizes.

The foregoing disclosure and showings made in the drawings are merelyillustrative of the principles of this invention and are not to beinterpreted in a limiting sense.

1. An apparatus for removing salts from a liquid comprising: a firstliquid containing at least one salt, magnetic composite particles, atank (2) for storing the first liquid containing at least one salt, amixing tank (4) in fluid communication with the tank (2) for mixing thefirst liquid containing at least one salt with the magnetic compositeparticles, and an electromagnetic separator (5) in fluid communicationwith the mixing tank (4), wherein the electromagnetic separator (5)comprises an electromagnetic source (6).
 2. The apparatus according toclaim 1 wherein the first liquid is an aqueous amine solvent.
 3. Theapparatus according to claim 2 wherein the amine solvent comprises atleast one of methyldiethanolamine and alkanolamine.
 4. The apparatusaccording to claim 1 wherein the at least one salt is formed by one ormore protonated amine cations and one or more anions selected from SCN″,HCOO″, CH3COO″, and CH3CH2COO—.
 5. The apparatus according to claim 1wherein the magnetic composite particles comprise iron oxide magneticparticles.
 6. The apparatus according to claim 1 wherein the magneticcomposite particles comprise alginate.
 7. The apparatus according toclaim 1 further comprising a second liquid for cleaning the magneticcomposite particles from adsorbed salt and a tank (3) in fluidcommunication with the mixing tank (4) for storing the second liquid,wherein the second liquid is preferably water.
 8. The apparatusaccording to claim further comprising a treated liquid tank (7) in fluidcommunication with the electromagnetic separator (5) for collectingfirst liquid which has been treated in the mixing tank (4).
 9. Theapparatus according to claim 1 further comprising a collecting tank (8)in fluid communication with the electromagnetic separator (5) and influid communication with the tank (3) for collecting the second liquidcontaining magnetic composite particles having at least a portion of theat least one salt adsorbed thereon.
 10. The apparatus according to claim1 wherein the first liquid is an aqueous amine solvent, preferablycomprising at least one of methyldiethanolamine and alkanolamine, the atleast one salt is formed by one or more protonated amine cations and oneor more anions selected from SCN˜, HCOO″, CH3COO″, and CH3CH2COO″, themagnetic composite particles comprise iron oxide magnetic particles andalginate, the apparatus further comprises a second liquid for cleaningthe magnetic composite particles from adsorbed salt and a tank (3) influid communication with the mixing tank (4) for storing the secondliquid, wherein the second liquid is preferably water; the apparatusfurther comprises a collection tank (7) in fluid communication with theelectromagnetic separator (5) for collecting first liquid which has beentreated in the mixing tank (4) the apparatus further comprises a treatedliquid tank (7) in fluid communication with the electromagneticseparator (5) for collecting first liquid which has been treated in themixing tank (4), and the apparatus further comprises a collecting tank(8) in fluid communication with the electromagnetic separator (5) and influid communication with the tank (3) for collecting the second liquidcontaining magnetic composite particles having at least a portion of theat least one salt adsorbed thereon. 11.-23. (canceled)